The information recording mechanism of a magnetographic recording apparatus may take on various configurations, such as one using an optical exposure station for selectively erasing (demagnetizing) a premagnetized recording medium (e.g. chromium oxide), or a configuration employing a magnetic write head through which a latent image of the information to be recorded is directly magnetically written onto the recording medium. (For a description of the general configuration of each of these types of recording schemes, attention may be directed to the U.S. Pat. No. 4,216,282, to Edwards et al for example.) In these configurations and in magnetographic recording apparatus in general, the fidelity with which the magnetic storage state of the magnetic recording medium can be accurately controlled is the principal factor for determining successful performance. While such fidelity is obviously an a priori requirement in an apparatus in which the recording mechanism constitutes a magnetic recording head, it also holds true in other configurations, such as one employing an optical exposure station, mentioned above, since that mechanism still requires a complete premagnetization of the entire recording surface and, to date, the principal expedient for accomplishing this task has been a magnetic head.
Now, although the manufacturing tolerances of the recording head can be controlled with precision, the surface of the recording medium, usually chromium dioxide, with which the magnetic head is intended to have effective intimate contact, usually does not have the desired, perfect geometric profile for establishing such effective intimate contact for any location on the recording surface. More particularly, the surface of the recording medium, (such as CrO.sub.2 layer, formed on the surface of a rotatable drum) typically contains imperfections including bumps and seams in the recording material itself, and contamination by foreign matter, such as dust and toner particles which, even with the provision of cleaning devices such as vacuum knives, may not be perfectly removed.
Because the quality of the image that is formed on the surface of the recording drum by the magnetic recording head depends on the degree of coupling between the recording head and the drum surface, imperfections on the surface of the recording medium, such as those exemplified above, may, depending upon drum rotational speed, constitute a source of degradation in both the image quality and the physical surface of the drum and/or the recording head during the movement of the drum past the head. Not only are imperfections on the drum surface a cause of head bounce, but because the head is under pressure to maintain contact and thereby maximum magnetic coupling between head and drum, both the head and the drum are subject to wear, and plate-out (the disposition of magnetic medium onto the magnetic head) may occur.
At low rotational velocities of the recording drum, the head can slide on the chromium dioxide layer without causing damage and without losing contact with the recording surface, so that the imperfections are not a serious problem. Also, at very high velocities, using a high quality magnetic disk or drum surface medium, the aerodynamic bearing that is created by the high relative rotational velocity between the recording surface and the head can be utilized in conjunction with the high quality medium to diminish the above problems. At a medium-range of velocities, however, (on the order of 50 to 150 inches per second, imperfections in the drum surface cannot be ignored, but instead, subject the imaging process to the above-mentioned drawbacks.
One proposed solution for solving the inadequacy of the use of an air bearing between the recording head and the surface of the recording medium involves the use of an oil bearing, such as that described in the U.S. Pat. Nos. 3,005,675 to Ledin et al and 2,969,435 to Lynott. In the recording mechanism described in these patents a film of oil is applied to the recording surface to prevent damage to the surface due to adhering metal and dirt particles and to eliminate frictional contact between the recording head and the drum surface, as the head is caused to effectively ride upon the oil bearing.
Where the recording medium is employed for the reproduction of the recorded information, as by transfer of an image of the recorded information to a sheet or web, as in a magnetographic recording/reproduction apparatus, the use of an oil bearing is not a viable solution to the problem, since the surface of the recording medium (drum) must be clean before the application of the image transfer material (toner) for each (successive) reproduction of the magnetically recorded image. Oil is an organic compound often derived from petroleum sources and, depending upon its grade, may have a boiling point over a wide range, e.g. 100.degree.-200.degree. C.; 175.degree.-275.degree. C.; and 250.degree.-400.degree. C. As a result, in a recording/reproduction apparatus oil is totally unsuited as a bearing material since the oil will only partial disappear through evaporation, as the higher-boiling components of the oil remain as residual films. If toner were applied to a oil-film containing drum the reproduction process would fail catastrophically.